1. Field of the Invention
The present invention relates to amorphous photoelectric transducers such as solar cells which use a p-n or p-i-n junction in an amorphous semiconductor to convert energy light, such as sunlight, to electric energy, as well as to a process for producing such transducers.
2. Description of the Related Art
In order to form an amorphous semiconductor having a p-n or p-i-n junction, p-type and n-type layers of amorphous semiconductor material, or p-type, i-type and n-type layers of amorphous semiconductor material, must be superposed, in this order or in the reverse order, on a substrate with an interposed electrode layer. Amorphous silicon (hereafter designated a-Si:H) is the best known of amorphous semiconductors. An amorphous silicon layer is typically formed on a substrate by a plasma assisted chemical vapor deposition (CVD) process in which a SiH.sub.4 based feed gas is decomposed within a plasma generated by a high frequency discharge on the order of 13.56 MHz, for example. In order to produce an a-Si:H layer having a desired conduction type, an appropriate dopant is mixed in the feed gas. For producing a p-type a-Si:H layer, diborane (B.sub.2 H.sub.6) or boron trifluoride (BF.sub.3) is used as the dopant. When the p-type layer is to be used as a window for admitting incident light, its optical band gap desirably is as large as possible to insure minimum light absorption by that layer.
However, when the impurity level of the p-type a-Si:H layer is controlled by plasma-assisted CVD with the feed gas containing a diborane dopant gas subjected to discharge at a high frequency such as 13.56 MHz, the hydrogen content of the p-type film decreases as the boron level increases and the resulting narrow optical band gap makes the p-type film unsuitable for use as the window of a photoelectric transducer. If BF.sub.3 is used as a dopant, the decrease in the hydrogen content of the film is smaller than when diborane is used, but, the strong binding of boron and fluorine atoms yields residual B-F bonds in the film that lower the degree of activation of boron atoms.